1. Field of the Invention
This invention relates to snowmobile skis.
2. Description of the Prior Art
Traditionally all snowmobile skis have been made of steel. A backbone is welded to the sole to form a closed box or an open U-shape.
Some skis, not for snowmobiles, have been made of reinforced plastics, plastics and wood or a combination of these materials.
Recently a snowmobile ski has been proposed by Ultimate Sports Inc. in which the ski is made of two main parts, namely a cast aluminum backbone or stiffener and a sole made of ultra high molecular weight-polyethylene (UHMW-PE). According to this design characteristics such as the static and dynamic coefficients of friction, dynamic stability and turning response of the ski can be determined by choice of material of the sole and profile of the sole, while characteristics such as ability to withstand static and dynamic loads are determined by design of the stiffener. By separating out these two different sets of parameters the ski design can be optimized.
The ski proposed by Ultimate suffers from the following disadvantages. Firstly, the bottom of the stiffener is flat and it rests on top of a flat upper surface of the sole. Thus, impacts on the sole are transmitted directly through to the stiffener which would have the effect of weakening the stiffener.
Secondly, when the ski is to be mounted to a suspension assembly of the snowmobile, the stiffener is thickened to increase the strength and rigidity at that point. However, the increase in thickness greatly increases the overall weight of the ski which is undesirable.
Thirdly, the UHMW-PE used in the sole is subject to wear.
Fourthly, the front handle of the ski is formed of a separate component, adding to manufacturing and assembly costs.
Fifthly, the use of cast aluminum for the main stiffener is more expensive compared to the use of a steel stiffener.